北极燕鸥是一种特别的鸟。迁徙时，它们从北极圈飞往南极圈，再飞回起点，整个旅程非比寻常，历时一年之久。这种鸟的迁徙路线在全球鸟类中属最长，但它们在途中也会停下来歇歇脚。北极燕鸥在英国北部繁殖，以北大西洋中部的鱼类为食，为漫长的旅程积攒体力。

Back in 2010, an international research team fitted tracking devices to birds they believed to be special – Arctic terns. And it turns out they were right, as described in US journal, PNAS. The Arctic tern has an extraordinary year-long migration from the Arctic Circle to the Antarctic Circle and back again.

What does this route look like? Arctic terns begin their migration in the Northern hemisphere in the summer, which is breeding season. As it gets colder and darker, turning to winter, the birds fly southward, parallel to the coast of South America or hugging the coast of the African continent to reach their winter feeding ground, the Antarctic Circle. And they do not always fly in a straight line. While heading back up north, their flight path mimics an S-shape which they follow to save energy while navigating the wind systems in the different hemispheres. This journey is a round-trip of up to 35,000km long, which makes the Arctic tern's migration the longest of any bird. Plus, they see more daylight than any other animal on Earth!

But, on this epic journey, the birds do take some well-deserved breaks. Heading northward, the population stops on the north and west coast of the UK to breed. A female lays one to three eggs in a nest, and after an incubation period of around three weeks, they hatch, and fluffy brown and grey chicks emerge. Meanwhile, the adult birds feed in the shallow coastal waters on fish, such as sand-eels. In contrast, while heading south, the birds appear to stop off in the middle of the North Atlantic Ocean, where they indulge on fish and zooplankton, preparing themselves for their long journey ahead.

So, if you ever see a little black and white bird with red legs and a red beak, show them some appreciation. They have flown a long way to see you!